Image forming apparatus with specialized sheet conveyance speed control

Abstract

An image forming apparatus has a sheet material conveying system for conveying the sheet material to an image forming device and has an image formation driving source for driving the image forming device. A control is provided to vary the speed at which the sheet material is conveyed by the image forming device according to the kind of sheet material used, to control the conveyance driving source and the image formation driving source such that the speed at which the sheet material is conveyed by the sheet material conveying system when an image is formed by the image forming device is substantially the same as the speed at which the sheet material is conveyed by the image forming device, and to control the conveyance system driving source and the image formation driving source such that the speed at which the sheet material is conveyed by the sheet material conveying system before image forming device starts to form an image is substantially the same as or faster than the speed at which sheet material is conveyed by the image forming device.

What is claimed is:  
     
       1. An image forming apparatus comprising: 
       image forming means including an image bearing member for bearing a toner image, and a sheet material supporting member for supporting a sheet material to which the toner image is transferred, and adapted to hold and convey the sheet material between the image bearing member and the sheet material supporting member to thereby transfer the toner image on the image bearing member to the sheet material;  
       sheet material conveying means for conveying the sheet material toward the image forming means;  
       registration means for correcting skew of the sheet material conveyed by the sheet material conveying means and conveying the sheet material to the image forming means with a predetermined timing;  
       an image formation driving source for driving the image forming means;  
       a conveyance system driving source for driving the sheet material conveying means and the registration means; and  
       control means which makes a speed at which the sheet material is conveyed by said image forming means variable according to the kind of sheet material, which makes a speed at which the sheet material is conveyed by said sheet material conveying means substantially the same as a speed at which the sheet material is conveyed by said image forming means when an image is formed on the sheet material by said image forming means, and which makes a speed at which the sheet material is conveyed by said sheet material conveying means substantially the same as or faster than a speed at which the sheet material is conveyed by the image forming means before image forming means starts to form an image on the sheet material.  
     
     
       2. An image forming apparatus according to  claim 1 , wherein the control means controls the conveyance system driving source such that the sheet material is conveyed to the image forming means by the registration means at a speed different from the speed at which the sheet material is conveyed to the registration means by the sheet material conveying means. 
     
     
       3. An image forming apparatus according to  claim 2 , wherein the control means controls the conveyance system driving source and the image formation driving source such that the sheet material is conveyed to the registration means by the sheet material conveying means at a speed higher than the speed at which the sheet material is conveyed by the image forming means. 
     
     
       4. An image forming apparatus according to  claim 3 , wherein the control means controls the conveyance system driving source such that after the forward end of the sheet material conveyed to the registration means abuts the registration means, the speed at which the sheet material is conveyed by the sheet material conveying means is changed from a first conveying speed to a second conveying speed which is lower than the first conveying speed, and that after the rear end of the sheet material has left the registration means, the speed at which the sheet material is conveyed by the sheet material conveying means is changed from the second conveying speed to the first conveying speed. 
     
     
       5. An image forming apparatus comprising: 
       image forming means including an image bearing member for bearing a toner image, and a sheet material supporting member for supporting a sheet material to which the toner image is transferred, and adapted to hold and convey the sheet material between the image bearing member and the sheet material supporting member to thereby transfer the toner image on the image bearing member to the sheet material;  
       sheet material conveying means for conveying the sheet material toward the image forming means;  
       registration means for correcting skew of the sheet material conveyed by the sheet material conveying means and conveying the sheet material to the image forming means with a predetermined timing;  
       an image formation driving source for driving the image forming means;  
       a conveyance system driving source for driving the sheet material conveying means and the registration means;  
       first drive transmitting means and second drive transmitting means for transmitting a drive from the conveyance system driving source to the sheet material conveying means at different transmission ratios;  
       transmission ratio switching means for switching drive transmission between the first drive transmitting means and the second drive transmitting means; and  
       control means which makes a speed at which the sheet material is conveyed by the sheet material conveying means variable and which controls the conveyance system driving source and the image formation driving source such that a speed at which the sheet material is conveyed by the registration means is substantially the same as the speed at which the sheet material is conveyed by the image forming means and which controls the transmission ratio switching means such that when the sheet material is conveyed to the registration means, the drive of the conveyance system driving source is transmitted to the sheet material conveying means through the first drive transmitting means, and that when the sheet material is conveyed to the image forming means by the registration means, the drive of the conveyance system driving source is transmitted to the sheet material conveying means through the second drive transmitting means.  
     
     
       6. An image forming apparatus according to  claim 5 , 
       wherein the transmission ratio switching means is an electromagnetic connecting means for electromagnetically connecting and cutting off the transmission of a rotation drive force,  
       wherein the first drive transmitting means is a rotation drive transmitting member the transmission of which is connected by the electromagnetic connecting means, and  
       wherein the second drive transmitting means is a rotation drive transmitting member which includes a one-way connecting means for exclusively transmitting rotation in one direction and whose reduction ratio is larger than that of the first drive transmitting means.  
     
     
       7. An image forming apparatus according to any one of claims  1  through  6 , wherein the control means controls the image formation driving source such that the sheet material is conveyed by the image forming means at two or more conveying speeds. 
     
     
       8. An image forming apparatus according to  claim 7 , wherein the control means has the function of varying the speed at which the sheet material is conveyed by the image forming means according to the kind of sheet material. 
     
     
       9. An image forming apparatus according to  claim 7 , wherein the image formation driving source includes different image formation driving sources respectively driving the image bearing member and the sheet material supporting member. 
     
     
       10. An image forming apparatus according to  claim 7 , wherein the image forming means includes: 
       a plurality of image bearing members, and  
       a sheet material sequential conveyance means for sequentially conveying the sheet material to the plurality of transfer nip portions as the sheet material supporting member,  
       wherein toner images respectively borne by the plurality of image bearing members are sequentially transferred to the sheet material conveyed by the sheet material sequential conveyance means.  
     
     
       11. An image forming apparatus according to  claim 10 , wherein the image formation driving source includes different image formation driving sources for respectively driving the plurality of image bearing members and the sheet material sequential conveyance means. 
     
     
       12. An image forming apparatus according to  claim 7 , further comprising a fixing means which holds and conveys a sheet material to which an unfixed toner image has been transferred to thereby fix the toner image to the sheet material, 
       wherein the fixing means is driven by the image formation driving source, and conveys the sheet material at a speed which is substantially the same as the speed at which the sheet material is conveyed by the image forming means.  
     
     
       13. An image forming apparatus comprising: 
       image forming means for conveying a sheet material and forming an image on a sheet material;  
       conveying means for conveying the sheet material toward the image forming means;  
       an image formation driving source for driving the image forming means;  
       a conveyance system driving source for driving the conveying means; and  
       control means which makes a speed at which the sheet material is conveyed by the image forming means variable according to a kind of sheet material, which makes a speed at which the sheet material is conveyed by the conveying means substantially the same as a speed at which the sheet material is conveyed by the image forming means when an image is formed on the sheet material by said image forming means, and which makes a speed at which the sheet material is conveyed by said sheet material conveying means substantially the same as or faster than a speed at which the sheet material is conveyed by the image forming means before image forming means starts to form an image on the sheet material.  
     
     
       14. An image forming apparatus according to  claim 13 , wherein the control means controls the conveyance system driving source such that the sheet material is conveyed at a speed higher than the speed at which the sheet material is conveyed by the image forming means before the sheet material is conveyed by the image forming means. 
     
     
       15. An image forming apparatus according to  claim 13 , wherein the control means has the function of varying the speed at which the sheet material is conveyed by the image forming means according to the kind of the sheet material. 
     
     
       16. An image forming apparatus according to  claim 13 , wherein the image forming means includes: 
       a plurality of image bearing members for bearing a different color toner image, and  
       a conveying belt for conveying the sheet material,  
       wherein the sheet material is conveyed between the image bearing members and the conveying belt by the conveying belt.  
     
     
       17. An image forming apparatus according to  claim 16 , wherein the image forming means further includes a fixing means for fixing an unfixed image to the sheet material, and 
       the image formation driving source for driving the image bearing members, the conveying belt, and the fixing means.